guest-diag: single-instance scanner start + full-re-assert backoff

r148 ran THREE guest scanners (pin_gr_stream install_and_start retried
while a partially-failed first attempt had already started one, and the
pid-file kill missed it). Each scanner re-asserted the whole CE pair set
every 2 s; with a fully fragmented pair set (descending PAs, one page per
line) that is ~2 k debugfs writes/s per scanner, and the guest hit load 19
with clients wedged spinning in userspace.

- pin_gr_stream._start_cmd: kill EVERY existing scanner first (pattern
  assembled at runtime with printf so the command's own cmdline cannot
  self-match), then start exactly one.
- guest_pin_stream._emit_ce_mem_delta: the full re-assert keeps its 1.5 s
  cadence for the first STREAM_FULLREM_FAST_S seconds of a mem's life (the
  client-switch flush race), then backs off to STREAM_FULLREM_SLOW_S (10 s)
  as a safety net. Configurable via env.

1 files changed, 10 insertions, 6 deletions

diff --git a/tools/guest-diag/pin_gr_stream.py b/tools/guest-diag/pin_gr_stream.py
index c0a8c9d..2e45bbf 100644
--- a/tools/guest-diag/pin_gr_stream.py
+++ b/tools/guest-diag/pin_gr_stream.py
@@ -62,12 +62,16 @@ def _start_cmd():
                              capture_output=True, text=True).stdout
     prefixes = os.environ.get("CLIENT_PREFIXES", "cdt,va,victory")
     vma_every = os.environ.get("STREAM_VMA_EVERY", "1")
-    return ("echo '%s' | base64 -d > /tmp/guest_pin_stream.py; "
-            "if [ -f /tmp/guest_pin_stream.pid ]; then "
-            "p=$(cat /tmp/guest_pin_stream.pid 2>/dev/null); "
-            "[ -n \"$p\" ] && grep -q guest_pin_stream "
-            "/proc/$p/cmdline 2>/dev/null && sudo kill $p 2>/dev/null; "
-            "fi; "
+    # Kill EVERY existing scanner, not just the pid-file one: a retry after
+    # a partially-failed first attempt (pid file not written yet) used to
+    # leave the first scanner alive, and multiple scanners each re-assert
+    # the whole CE pair set - r148 ran three and drove the guest to load 19
+    # (clients wedged in userspace spins). The pattern is assembled at
+    # runtime via printf so this command's own cmdline (which contains the
+    # literal file path) cannot match the pkill.
+    return ("P=$(printf 'guest_pin_%%s.py' stream); "
+            "sudo pkill -f \"$P\" 2>/dev/null; sleep 1; "
+            "echo '%s' | base64 -d > /tmp/guest_pin_stream.py; "
             "sudo rm -f /tmp/guest_pin_stream.pid; "
             "sudo setsid nohup env CLIENT_PREFIXES='%s' "
             "STREAM_VMA_EVERY='%s' "